It has a fairly obvious association with the holocaust, but also just a genuine wtf were they thinking from Nike marketing types.The colouring is too ridiculous to even discuss, for me, but I'll engage on the wording. "Never Again" has been connected to a lot of different things. Since this is about the marathon, it's obviously connected to the "I'm never doing that again" that many marathon runners apparently utter at the end of it. But it's also been used for 9/11 in the US, and Pearl Harbour before that. In Norway it refers to the German invasion on April 9th 1940. Before that it probably had some other meaning.
Unless the ad went up literally on Holocaust Rememberance Day or something, I don't see how there's an obvious association with the Holocaust.